1. Field of the Invention
The present invention relates to a dual chamber pacing system normally operating in an atrial synchronized mode of the type having a mode switch to switch the pacing mode to a non-atrial synchronized ventricle stimulating mode in response to the detection of an atrial tachyarrhythmia and to switch the pacing mode back to the atrial synchronized mode in response to or after a preset time of the detection of ceased atrial tachyarrhythmia.
2. Description of the Prior Art
A dual chamber pacing system, i.e. a DDD-R system, should not track the atrial activity during atrial tachyarrhythmia including atrial fibrillation (AF). The pacing mode should in this case be changed to VVI-R. In U.S. Pat. No. 5,893,882 a pacemaker is described that is provided with a mode switching feature adapted to stabilize the ventricular heart rate during atrial fibrillation. In response to detection of atrial fibrillation the device therefore switches into a non-atrial synchronized ventricular rate stabilization pacing mode. The device remains in this mode of operation as long as the atrial fibrillation remains and during a preset time thereafter.
A problem arises for a patient having a pacemaker with a mode switching feature of this known kind, if the tachyarrhythmia or AF changes from paroxysmal, i.e. intermittent, seizures to a chronically, i.e. permanent, state between the follow-up tests of the system before a doctor. The pacing system will then continuously change mode between DDD and VVI. The tracking of atrial activity causes irregular stimulation rates with high rates which are not needed. Undersensing of atrial activity will in this case even sometimes worsen the situation for the patient, since when each atrial activity is not sensed the pacemaker will not be properly inhibited with irregular heart rates as a result.
There are normally several months between the follow-up tests by a doctor and in case of a state of chronicle tachyarrhythmia or AF the above situation of continuous mode switching between DDD and VVI will remain for such a comparatively long time causing the patient considerable discomfort before the doctor reprograms the pacemaker in connection with testing of the system. Consequently, tracking of a fibrillating atrium has to be avoided and in the case of a chronic tachyarrhythmia or AF state, the VVI-R mode of operation is the preferred stimulation mode.